Electric Fuel Pumps

[peterc]

Since there seems to be a lot of electric fuel pump questions being bandied about, I thought I'd add mine to the mix.

I have three (count'em, three) electric fuel pumps from various ZX's that all run (i.e. motors run fine when hooked up to to a battery), but don't/won't pump gas. (I figured I'd test them BEFORE installing them, to save myself some grief).

Figuring that there must be some crud builtup inside the pumps, or maybe cracked or worn out o-rings, I dissassembled one. The pump itself is an extemely simple design, consisting of a rotor with 5 cylindrical "pellets" and two 2 o-rings.

The o-rings looked fine and there was no varnish or crud inside and the check valve on the outtake nipple seemed to be working fine.

I replaced the o-rings anyway and reassembled the pump, but again it spun freely but wouldn't pump. My first thought was that I hadn't tightened the screws back on properly and wasn't getting a good seal. So I replaced the original machine scews with new ones (allen-keyed) and carefully torqued them down, so I don't think that's the problem. Still no luck.

Thinking that I'd re-assembled it incorrectly, I VERY carefully took apart the second one. It too looked fine. I re-assembled the first pump ensuring the all parts were put back exactly as per the second pump, but again, same results.

Rapidly running out of possibilites, I then removed the casing itself. There are no other pump related parts in there, only the electric motor and the exit nipple (I'm assuming it's designed this way so the gasoline cools the motor as it's pumping).

I used a 2 gallon gas can, the original nissan intake hose (goes from the tank to the inlet side of the pump, and it's in good condition BTW, no cracks or leaks), and then 2 feet of gas hose on the exit side of the pump going to another gas can.

I've tried placing the gas can higher than the pump (as per in-car installation) and level with the pump to no avail. I've even tired reversing the polarity on the pump (i.e. hooked the neg. post of the pump to the positve post on the battery) and sticking the exit hose into the can of gas (desperate or what??). Nothing.

I know the oil pump needs to be primed prior to installation but surely this can't be the case with the fuel pump or we'd be in a real mess every time we run out of gas.

Anyone had any experience working with these pumps? Is there a special incantation the needs to be invoked prior to re-assembly? Considering how simple the design is, I can't believe I'm having so much trouble getting one to work.

[V8-240Z]

What about the screeen that is inside the pump inlet port?

[peterc]

There doesn't appear to be a screen per se, on the inlet side (or the outlet side for that matter). There is a little plastic knobby thing inside the inlet tube but it sure doesn't look like there's a screen there. Either way, the inlet tube is definitely not blocked in any way.

[V8-240Z]

Give this a shot, Does it look like what you have?

http://63.230.165.175:8884/Files/Datsun/Fuel/Fuel-Filter/screen.jpg

Here is another one

http://63.230.165.175:8884/Files/Datsun/Fuel/Fuel Pump Fix.htm

I have a couple of those pumps here and I can see no

reason for it not to work.

Dave

[260Zed]

I know the oil pump needs to be primed prior to installation but surely this can't be the case with the fuel pump or we'd be in a real mess every time we run out of gas.

I'd try it primed, then at least you know if it works at all.

Luke

[sblake01]

Those pumps are self priming. What you did should work as long as you re assembled it correctly and it was working in the first place. I've replaced o rings in them and re assembled them and they worked fine. Your scenario has me stumped since, as you say, they are very simplistic in design and I have done exactly what you described several times in the past and they always worked for me.

[hls30.com]

I have always found that once the internals of the fuel pump are dry, pouring a little gas into it gets things moving again-where as letting it pull its own prime is a lesson in frustration-but ultimately, it does self prime-just takes a good while longer than I wan to hear it run dry!

Will

[sblake01]

I'm not sure about the carb pumps but the efi pumps pull fuel immediately.

[peterc]

Thanks for the suggestions guys. I'll take a closer look at the inlet screens (didn't realize what they were ), although they're definitely not blocked as you can blow through them quite easily.

I'll also try priming the pumps first. Maybe I just wasn't letting them run long enough, though they seem to self-prime quite fast whenever you run out of gas.